docs: Add C++ unordered_set::cbegin() term entry (#8031)

Author: Rishabh1925

content/cpp/concepts/unordered-set/terms/cbegin/cbegin.md

@@ -0,0 +1,99 @@
+---
+Title: '.cbegin()'
+Description: 'Returns a constant iterator pointing to the first element of the unordered_set.'
+Subjects:
+  - 'Computer Science'
+  - 'Programming'
+Tags:
+  - 'C++'
+  - 'Unordered Set'
+  - 'STL'
+  - 'Iterators'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+The **`.cbegin()`** method returns a **constant iterator** that points to the first element in an `std::unordered_set`.
+
+The key feature of a constant iterator (`const_iterator`) is that it allows you to **read** the elements but **prevents** you from modifying them. This is a best practice when iterating over a set to ensure data integrity. Since `unordered_set` does not guarantee any specific order, the element returned by `cbegin()` depends on the internal hash table structure.
+
+## Syntax
+
+The `.cbegin()` method is called directly on the `unordered_set` object.
+
+```cpp
+unordered_set_name.cbegin();
+```
+
+## Parameters
+
+The method takes no parameters.
+
+## Return Value
+
+Returns a `const_iterator` (constant iterator) pointing to the first element in the `unordered_set`.
+
+## Example
+
+This example demonstrates obtaining the starting element of an `unordered_set` using `cbegin()`. Note that attempting to modify the element pointed to by the `const_iterator` would result in a compilation error.
+
+```cpp
+#include <iostream>
+#include <string>
+#include <unordered_set>
+#include <algorithm> // Required for std::find or general use
+
+int main() {
+  std::unordered_set<int> unique_numbers = {10, 5, 20, 15};
+  
+  // Get a constant iterator to the beginning
+  auto it = unique_numbers.cbegin();
+
+  // Print the value of the first element (read-only access)
+  std::cout << "The first element in the set's internal order is: " << *it << "\n";
+
+  // Advance the iterator to the next element
+  // Note: The order of elements is not guaranteed!
+  ++it; 
+
+  std::cout << "The second element is: " << *it << "\n";
+
+  // The following line would cause a compile-time error:
+  // *it = 99; 
+
+  return 0;
+}
+```
+
+Output:
+
+```
+The first element in the set's internal order is: 20
+The second element is: 5
+```
+
+## Codebyte
+
+Use the Codebyte below to access the first element of an `unordered_set` using the constant iterator returned by `.cbegin()`.
+
+```cpp
+#include <iostream>
+#include <unordered_set>
+
+int main() {
+  std::unordered_set<std::string> colors = {"red", "green", "blue", "yellow"};
+  
+  // Use cbegin() to get the constant iterator
+  auto start_it = colors.cbegin();
+  
+  // Print the value the iterator points to
+  std::cout << "First element: " << *start_it << "\n";
+  
+  // Advance the iterator
+  ++start_it;
+  std::cout << "Second element: " << *start_it << "\n";
+
+  return 0;
+}
+```